1. Field of the Invention
The present invention relates to styrenic polymers, and specifically to non-staining, non-sticking styrenic polymers.
2. Description of Prior Art
It is well known in the art to produce various shaped articles from polystyrene monomers. These articles, however, suffer from an assortment of defects, such as low resistance to fat-containing foods, i.e., low environmental stress-crack resistance to fatty acids, oils and grease, which act as a cracking agent.
It is now known that polymers containing para-methylstyrene (PMS), and especially high impact poly(p-methylstyrene) (HIPPMS) overcome the above-mentioned defects and are advantageous in other areas as well. See, for example, "A Better Styrene Goes Commercial", Chemical Week, Feb. 17, 1982, pages 42-46.
Even though there are characteristic advantages of one styrenic polymer over another, there are some disadvantages which are common to all styrene polymers. For example, many styrenic polymers are susceptible to staining by staining agents, such as oil, grease or fatty acids. Additionally, while many of the characteristics of HIPPMS are superior to other styrenes, HIPPMS is particularly susceptible to staining, presumably due to the high affinity of the methyl groups in HIPPMS towards fatty acids, etc.
The staining agents initiate the staining process when they are applied to the polymer surface, which is followed by diffusion of plasticization through the bulk of the copolymer. Thus, the surface of the styrenic polymer plays a significant role in whether or not the polymer will be stained.
It is an object of the present invention to modify the surface of styrenic polymers.
It is another object to improve environmental stress-crack resistance properties of styrene copolymers.
It is further an object to minimize the surface wettability of the above-mentioned cracking agents on styrenic polymer surfaces by the modification of these polymers.
It has been found that styrenic copolymers can be synthesized in situ with siloxanes, preferably having a molecular weight in excess of 20,000, in order to form a non-removable, non-staining, non-sticking surface on the base styrenic copolymer.